Of course this episode introduces the Jem'Hadar, who will feature heavily in the future Dominion war.

Plotline

On a routine trip into the Gamma Quadrant, Sisko and Quark are imprisoned by the Jem'Hadar, genetically engineered soldiers of the Dominion. Starfleet rides to the rescue - but in a pitched battle, the Jem'Hadar prove to have a considerable lead in both technology and determination.